Answer:
Due to a unique stage in meiosis called Pachytene.
Step-by-step explanation:
In this stage, a process called crossing-over occurs, which is an exchange of genetic material between non-sister chromatids. This stage begins when synapsis is complete. The DNA of two sister chromatids -one maternal and one paternal- is broken by specific proteins. the DNA breaks are closed up so that each broken end is joined to the corresponding segment of the non sister chromatid. Thus, a parental chromatid is joined to a piece of maternal chromatid and vise versa.
Variation It distinguishes one creature from another. Natural selection requires variation. Variations in an organism's species aid in adaptation to the environment and assist to avert extinction.